400 
Cast Steel . 
will not exhibit those changes of colour which take place 
when the other methods are employed. The following* 
table shows the temperature at which the various colours 
make their appearance. 
430° to 450° indicates the several tints of straw colour, 
and is the temper for razors and those intruments which 
have a stout back supporting a keen and delicate edge. 
470° corresponds with the full yellow, and is the pro- 
per temper for scalpels, pen-knives, and other fine-edged 
instruments. 
490° indicates the brown yellow, and is the proper 
temper for scissars and small shears. 
510° indicates the first tinge of purple, and is the tern- 
per for pocket and pruning-knives. 
530° indicates purple, and is the temper for table 
and carving-knives. 
550 d to 560° indicates the different shades of blue, and 
is the temper for watch-springs, swords, and all those in- 
struments in which great elasticity is required. 
600° corresponds with black, and is the lowest degree 
of temper. 
One great advantage attending the use of cast steel is 
its uniform quality : the carbon which it contains appears 
to be equally distributed through every part of the same 
mass in consequence of the fusion that it has undergone : 
whereas both the natural steel and the steel of cementation, 
are apt to contain veins of iron, either quite soft or at most 
very slightly carburetted, and thus a degree of imperfec- 
tion and uncertainty is introduced extremely mortifying 
to the artist, and not unfrequently the occasion of much 
labour in vain. It is therefore no small benefit which Mr. 
Nicholson has conferred on the workers in iron and steel 
by publishing a simple and effectual method of ascertain- 
ing whether any particular bar is pure iron or steel or a 
mixture of both* The surface of the metal being cleaned 
